cppc = [ cppd[0], cppb[1] ];
cpph = cppd + [0,-1] * catch_stalk_h;
cppe = cppd + [0,-1] * (catch_knob_above_gap + catch_knob_dia/2);
cppc = [ cppd[0], cppb[1] ];
cpph = cppd + [0,-1] * catch_stalk_h;
cppe = cppd + [0,-1] * (catch_knob_above_gap + catch_knob_dia/2);